Lipoprotein(a), (Lp(a)], has been considered an important independent genetic determinant of cardiovascular disease in Caucasians; however, the role of Lp(a) in cerebrovascular disease, especially in African Americans and Hispanics, is less clear. Preliminary data in a sample of patients and controls from northern Manhattan indicates that Lp(a) confers an increased risk of ischemic stroke (OR=3.0). A population-based case-control study is proposed to investigate the following primary aims: (1) Lp(a) is an independent predictor of first ischemic stroke, particularly atherosclerotic ischemic cerebral infarction; (2) Lp(a)'s role in cerebrovascular disease is influenced by other known stroke risk factors; and (3) Serial Lp(a) levels do not vary following ischemic cerebral infarction. Secondary aims are to determine whether Lp(a) is causally associated with extracranial internal carotid atherosclerosis, to characterize the distribution of serum Lp(a) levels in stroke-free controls of three race/ethnic groups, and to prospectively determine whether elevated Lp(a) levels are predictive of outcome after stroke. A total of 800 cases of ischemic stroke and 800 stroke-free controls will be enrolled in this 5-year study. Subjects will be drawn from the ongoing study "Stroke Incidence and Prognosis in a Mixed Ethnic Region" (NINDS RO1 29993). Evaluation of Lp(a) will be measured using an immunonephelometric assay, carotid atherosclerosis will be diagnosed by Duplex Doppler, and diagnosis of cerebral infarction subtypes will be made by a diagnostic committee. Odds ratios will be calculated, and conditional logistic regression will be used to judge the independent significance of the main exposure variable, Lp(a), and other stroke risk factors.